Understanding the mechanical properties of two-phase nanocrystalline AlCrFeMoNbNi high-entropy alloy evaluated by nanoindentation

Nanocrystalline two-phase AlCrFeMoNbNi high-entropy alloy (HEA) was produced using mechanical alloying (MA) and high-pressure torsion (HPT), with an average grain size of 10 ± 2 nm. Nanoindentation testing was performed to measure the hardness from which the strengthening contributions via various mechanisms such as strain hardening, solid solution strengthening, frictional stress and grain boundary strengthening are assessed. A Hall–Petch coefficient of 0.135 MPa \(\sqrt{\text{m}}\) $\sqrt{\text{m}}$ is estimated from this analysis, which is much lower than that for comparable alloys. A very low activation volume, for plastic deformation, of 3.4 b³ was measured from strain rate dependent nanoindentation testing, which is indicative of grain boundary mediated plastic deformation. Furthermore, the estimated activation energy of 171 kJ/mol measured from nanoindentation testing, is comparable to that for grain boundary diffusion in Cantor alloy. These experimental results provide insights on the deformation response of nanocrystalline two-phase AlCrFeMoNbNi HEA at an extremely fine grain size of around 10 nm.